While most of the prior art in the field of spiral binding apparatus relates to the use of metallic wire spirals, two patents specifically relate to the use of plastic spirals. U.S. Pat. No. 2,638,609 of Penner describes a machine for binding books with special features for aligning the perforations of a sheaf of papers to be bound and to confine the travel of the plastic spiral binding material. U.S. Pat. No. 4,249,278 of Pfaffle describes a machine for spiral binding which feeds plastic thread from a bulk spool, softens the thread, winds it on a mandrel to form a spiral, cools it to harden and then feeds the rigid spiral into a perforated sheet group.
Pfaffle '278 integrates the process of the forming of plastic spiral binding coils from plastic thread with that of a binding machine to produce an end product of spiral bound books. Plastic thread is pulled from a spool, preheated, wound around a mandrel in a heated zone, continuously fed into a cooling sleeve for rapid cooling by exposure to a blast of cold air generated by a vortex cooler and then the spiral is fed into the binding machine. However, in Pfaffle '278 the plastic coil material of polyvinyl-chloride (PVC) can become brittle by the rapid cooling, since it develops voids in its interior. The resulting spiral coil is too brittle to process in a book binding machine since the ends are broken off during the bending process or in early use of the bound books by the ultimate consumer.
Other patents relating to spiral binding machines include U.S. Pat. No. 4,378,822 of Morris which describes a spiral binding machine with a drive component. However, the mandrel of Morris '822 is fixed, not laterally adjustable as in the present invention, and the mandrel of Morris '822 has a closed end, which requires pre-feeding of the spiral thereon.